My diabetic patient complains of acute blurred vision past few days since her blood glucoses have been out of control. How does high blood glucose affect the vision acutely?

“Vision loss or blurriness” is one of the most common manifestations of acute hyperglycemia in diabetic patients and is due to the osmotic swelling of the lens resulting in changes in its characteristics and the inability to properly focus an image.1

Since glucose acts as a solute, an increase in the concentration of glucose causes a rise in osmotic forces and movement of fluid into the lens, resulting in transient myopia. Interestingly, the increase in the fluid in the lens causes a change in its refractory index which is associated with focusing an image at a different length; it does not affect its curvature or position.

Baseline vision should be eventually restored by correcting glucose levels.2 Also remember that rapid correction of hyperglycemia may make the lens swelling worse, causing increased visual disturbances.3

Fun fact: Did you know that chronic hyperglycemia is associated with cataract formation due to excess conversion of glucose to sorbitol in the lens? 4